Electro-dip coating method

ABSTRACT

Use of water-insoluble organic nitrites and/or nitrates as additives for electrodeposition coating compositions, and process for the production of an electrodeposition lacquer with improved adhesion for subsequent coats in which one or more water-insoluble organic nitrites and/or nitrates is added to the electrodeposition coating composition and the coating film obtained by electrodeposition is stoved in an indirectly heated circulating air oven.

This application is a 35 USC 371 National Stage application ofPCT/EP00/11951 filed Nov. 29, 2000.

BACKGROUND OF THE INVENTION

The invention concerns a process for cathodic electrodeposition coating(CEC) using water-insoluble organic nitrites and/or nitrates asadditives for the cathodic electrodeposition coating compositions inorder to improve the adhesion of subsequent coats to coatings producedfrom them.

Cathodic electrodeposition lacquers (CEC lacquers) are used inparticular for producing anti-corrosive primers on metallic substrates,such as car bodies for example. The coating films deposited fromelectrodeposition lacquers by electrodeposition are then stoved in largecirculating air ovens, which can be heated directly or indirectly, andprovided with further coating films. Directly heated circulating airovens are heated by combustion of natural gas, for example, whereby thewaste gases are introduced into the circulating air of the oven. Incirculating air ovens heated indirectly by means of heat exchangers, nowaste gases are introduced into the circulating air of the oven.

It has been established in industrial practice that the adhesion ofsubsequent coating films applied to stoved cathodic electrodepositioncoating films, especially underbody sealant films, is often inadequateif the cathodic electrodeposition primer has been stoved in indirectlyheated circulating air ovens.

The object of the invention is the improvement or provision of anadequate adhesion of coating films to cathodic electrodeposition coatingfilms that have previously been stoved in indirectly heated circulatingair ovens. This applies particularly in connection with underbodysealant films for application onto cathodic electrodeposition coatingfilms.

The object can be achieved if cathodic electrodeposition lacquerscontaining scarcely volatile or non-volatile, water-insoluble organicnitrites and/or nitrates are used for cathodic electrodeposition coatingfilms that are to be stoved in indirectly heated circulating air ovensfollowing electrodeposition.

Although JP 52127930 describes electrodeposition coating compositionsthat can contain various cellulose derivatives, such as e.g. cellulosenitrate, no reference is made to an improvement of the adhesion ofsubsequent coats to coatings obtained from electrodeposition coatingcompositions containing organic nitrite and/or nitrate.

DE 36 14 599 C describes a process for stoving cathodicelectrodeposition lacquers containing flow-promoting additives in anindirectly heated oven, whereby fillers or underbody sealants forexample are applied to the stoved electrodeposition lacquer. A contentof nitrogen oxides of at least 1 mg/m³ is established in the oven. Thisminimum content of nitrogen oxides is necessary to improve the adhesionbetween the cathodic electrodeposition film and the other coats.

SUMMARY OF THE INVENTION

The present invention provides a process for producing anelectrodeposition coating film with improved adhesion for subsequentcoats by cathodic deposition of a coating film from a cathodicelectrodeposition coating composition onto an electrically conductivesubstrate and stoving, characterised in that one or more water-insolubleorganic nitrites and/or nitrates is added to the cathodicelectrodeposition coating composition and stoving is performed in anindirectly heated circulating air oven, whereby the proportion of freshair introduced into the circulating air oven is 0 to 20 vol. % of theair in the oven.

The invention also provides a process in which a subsequent coat, inparticular a conventional underbody sealant film, is applied to thecoating film obtained as above.

DETAILED DESCRIPTION OF THE INVENTION

The expression “water-insoluble organic nitrites and/or nitrates” issubstituted below by the abbreviated form “nitrites and/or nitrates”.

The cathodic electrodeposition coating compositions used according tothe invention are aqueous coating compositions having a solids contentof for example 10 to 30 wt. %. The solids content in the cathodicelectrodeposition coating compositions is formed from the resin solids,pigments, fillers, other conventional lacquer additives and the contentof nitrites and/or nitrates that is substantial to the invention. Theresin solids in the cathodic electrodeposition coating compositionsconsist of the binder(s) and any crosslinker resin(s) that is/areoptionally included. Any pigment paste resins (paste resins) optionallyincluded in the cathodic electrodeposition coating compositions arecounted with the binders. At least a part of the binders carries ionicsubstituents and/or substituents capable of conversion to ionic groups.The binders can be self-crosslinking or externally crosslinking, in thelatter case they carry groups capable of chemical crosslinking and thecathodic electrodeposition coating compositions then containcrosslinking agents. The crosslinking agents can also display ionicgroups.

The ionic groups or groups of ionic binders capable of conversion toionic groups are cationic groups or groups capable of conversion tocationic groups, e.g. basic groups, preferably nitrogen-containing basicgroups; these groups can be in quaternised form or are converted tocationic groups with a conventional neutralising agent, e.g. a sulfonicacid such as amidosulfonic acid or methane sulfonic acid or an organicmonocarboxylic acid, such as formic acid, acetic acid or lactic acid.Examples are amino, ammonium, e.g. quaternary ammonium, phosphoniumand/or sulfonium groups. Amino groups that are present can be primary,secondary and/or tertiary. The groups that can be converted to ionicgroups can be in partially or wholly neutralised form.

The binders carry conventional functional groups capable of chemicalcrosslinking, for example hydroxyl groups, corresponding for example toa hydroxyl value of 30 to 300, preferably 50 to 250 mg KOH/g.

The cathodic electrodeposition coating compositions used according tothe invention are known per se. They contain conventional binders thatare capable of cathodic deposition, for example resins containingprimary, secondary and/or tertiary amino groups. Their amine values are20 to 250 mg KOH/g, for example. The weight-average molecular weight(Mw) of these cathodic electrodeposition binders is preferably 300 to10,000. The resins can be converted to the aqueous phase afterquaternisation or neutralisation of at least a part of the basic groups.Examples of such cathodic electrodeposition binders are aminoepoxyresins, aminoepoxy resins with terminal double bonds, aminoepoxy resinswith primary OH groups, aminopolyurethane resins, amino group-containingpolybutadiene resins and/or modified epoxy resin-carbon dioxide-aminereaction products and amino(meth)acrylate resins. The cathodicelectrodeposition binders can be self-crosslinking by conventional meansor they are used in combination with known crosslinking agents. Examplesof such crosslinking agents are amino resins, blocked polyisocyanates,crosslinking agents with terminal double bonds, polyepoxy compounds orcrosslinking agents containing groups capable of interesterification.

The cationic binders can be used as a cathodic electrodeposition binderdispersion, which can contain crosslinking agents, to produce thecathodic electrodeposition coating compositions used according to theinvention. Cathodic electrodeposition binder dispersions can be producedby synthesis of cathodic electrodeposition binders in the presence orabsence of organic solvents and conversion to an aqueous dispersion bydilution with water of the cathodic electrodeposition bindersneutralised with neutralising agent. The cathodic electrodepositionbinder(s) can be mixed with one or more suitable crosslinking agents andconverted along with these into the aqueous dispersion. Organic solvent,if present, can be removed down to the desired content before or afterconversion to the aqueous dispersion, by vacuum distillation forexample. The subsequent removal of solvents can be avoided for exampleif the cathodic electrodeposition binders optionally combined withcrosslinking agents are neutralised with neutralising agent in alow-solvent or solvent-free state, e.g. as a solvent-free melt attemperatures of up to 140° C. for example and then converted to thecathodic electrodeposition binder dispersion with water. Removal oforganic solvents can likewise be avoided if the cathodicelectrodeposition binders are prepared as absolution in one or moreradically polymerisable, olefinically unsaturated monomers or if thebinders are synthesised in one or more radically polymerisable monomers(e.g. styrene) as solvent, are then converted to an aqueous dispersionby neutralising with neutralising agent and diluting with water and theradically polymerisable monomers are then removed by polymerisation.

The cathodic electrodeposition coating compositions used according tothe invention contain nitrites and/or nitrates particularly in asufficient quantity such that a coating film, in particular an underbodysealant film for example, subsequently applied to the cathodicelectrodeposition coating film stoved in an indirectly heatedcirculating air oven displays an adequate adhesion. The nitrites and/ornitrates are contained in the cathodic electrodeposition coatingcompositions corresponding for example to a content of 0.05 to 0.5 wt. %nitrogen in the form of organically bonded nitrite and/or nitrate,relative to the resin solids.

The nitrites and/or nitrates are esters of nitrous acid or of nitricacid with alcohols, such as e.g. low-molecular mono- or polyalcohols,but particularly esters of nitrous acid or of nitric acid of mono- orpolyhydroxy-functional polymers. Nitrates are preferred.

In particular they are compounds that are scarcely volatile ornon-volatile under the conditions of formulation and application and ofstoving of the electrodeposition lacquers. By reason of theirwater-insolubility the nitrites and/or nitrates can be depositedtogether with the other components constituting the solids in thecathodic electrodeposition coating composition by electrodeposition fromthe cathodic electrodeposition coating compositions onto electricallyconductive substrates.

An example of a nitrate that is particularly preferably used in thecathodic electrodeposition coating compositions used according to theinvention is cellulose nitrate with a nitrogen content in the form oforganically bonded nitrate of 6.7 to 12.5, preferably 10.5 to 12.5 wt.%. If the particularly preferred cellulose nitrate with a nitrogencontent of 10.5 to 12.5 wt. % is used as a non-volatile, water-insolubleorganic nitrate in the cathodic electrodeposition coating compositionsused according to the invention, its content is for example 1 to 4 wt.%, relative to the resin solids in the cathodic electrodepositioncoating composition. For the purposes of the present invention cellulosenitrate can be used as a product wetted with alcohol, for examplebutanol, or as an organic solution in solvents such as e.g. alcohols,esters, ketones, glycol ethers, glycol esters, glycol ether esters andmixtures thereof. If there is no objection to plasticisers in thecathodic electrodeposition coating, commercial cellulose nitratedesensitised with plasticiser can also be used for the purposes of thepresent invention.

As is described in more detail below, the nitrites and/or nitrates canbe added to the cathodic electrodeposition coating compositions invarious ways, for example at the start during production of the cathodicelectrodeposition coating compositions used according to the inventionor subsequently, for example directly before or during use inelectrodeposition coating.

In addition to the binder(s), water and the content of nitrites and/ornitrates that is substantial to the invention and the crosslinking agentthat is optionally present, the cathodic electrodeposition coatingcompositions used according to the invention can contain pigments,fillers, solvents and/or conventional lacquer additives.

Examples of pigments are conventional inorganic and/or organic pigments,such as e.g. titanium dioxide, iron oxide pigments, carbon black.Examples of fillers are kaolin, talc or silicon dioxide. The cathodicelectrodeposition coating compositions can also contain anti-corrosivepigments. Examples of these are zinc phosphate or organic corrosioninhibitors.

Pigments and/or fillers can be dispersed in a part of the binder andthen ground in a suitable unit, e.g. a bead mill, after which theprocess is completed by mixing with the outstanding portion of binder.The cathodic electrodeposition coating composition or bath can then beproduced from this material by dilution with water—after addition ofneutralising agent if this has not already taken place (one-componentprocedure).

Pigmented cathodic electrodeposition coating compositions or baths canalso be produced by mixing a cathodic electrodeposition binderdispersion and a separately produced pigment paste, however(two-component procedure). To this end a cathodic electrodepositionbinder dispersion is further diluted with water, for example, and anaqueous pigment paste then added. Aqueous pigment pastes are produced bymethods known to the person skilled in the art, preferably by dispersingthe pigments and/or fillers in paste resins conventionally used forthese purposes.

The ratio by weight of pigment plus filler/binder plus crosslinkingagent in the cathodic electrodeposition coating compositions usedaccording to the invention is for example from 0:1 to 0.8:1, forpigmented lacquers it is preferably between 0.05:1 and 0.4:1.

The cathodic electrodeposition coating compositions used according tothe invention can optionally contain other additives in addition to thenitrites and/or nitrates, for example in proportions of 0.1 to 5 wt. %,relative to the resin solids. These are in particular such examples thatare known for cathodic electrodeposition coating compositions, forexample wetting agents, neutralising agents, flow control agents,catalysts, corrosion inhibitors, antifoam agents, light stabilisers,antioxidants, and conventional anti-crater additives. The additives canbe introduced into the cathodic electrodeposition coating compositionsin any way at all, for example during binder synthesis, duringproduction of cathodic electrodeposition binder dispersions, by means ofa pigment paste or separately.

The cathodic electrodeposition coating compositions used according tothe invention can also contain conventional solvents in the conventionalproportions for cathodic electrodeposition coating compositions. Suchconventional solvents for cathodic electrodeposition coatingcompositions are for example glycol ethers, such as butyl glycol andethoxy propanol, and alcohols, such as butanol. The solvents can beintroduced into the cathodic electrodeposition coating compositions byvarious means, for example as a component of binder or crosslinkingagent solutions, via a cathodic electrodeposition binder dispersion, asa component of a pigment paste or by separate addition. The solventcontent of the cathodic electrodeposition coating compositions is forexample from 0 to 5 wt. % inclusive, relative to cathodicelectrodeposition bath capable of being used for coating.

The cathodic electrodeposition coating compositions used according tothe invention can be prepared by the known methods for producingcathodic electrodeposition baths, i.e. in principle both by means of theone-component procedure described above and by means of thetwo-component procedure.

The cathodic electrodeposition coating compositions used according tothe invention can be produced for example in such a way that thenitrites and/or nitrates are mixed as supplied or as an organic solutionwith the other components of the cathodic electrodeposition coatingcomposition. The nitrites and/or nitrates can be added to the cathodicelectrodeposition coating compositions in various ways, for example atthe start during production of the cathodic electrodeposition coatingcompositions or subsequently.

For example they are first mixed with binders before the othercomponents are incorporated.

Production of the cathodic electrodeposition coating compositions usedaccording to the invention by the one-component procedure can beperformed for example in such a way that the nitrites and/or nitratesare in the presence of the components of the cathodic electrodepositioncoating composition that are in the non-aqueous phase and are convertedwith them to the aqueous phase by dilution with water. Pigments and/orfillers can for example be dispersed in a part of the binder and/orcrosslinking agent and then ground in a suitable unit, e.g. a bead mill,after which the process is completed by mixing with the outstandingportion of binder and/or crosslinking agent. The nitrites and/ornitrates can be included in the binder and/or crosslinking agent usedfor dispersion and/or for completion. The cathodic electrodepositioncoating composition or bath can then be produced from the material thusobtained by dilution with water—after addition of neutralising agent ifthis has not already taken place.

Production of the cathodic electrodeposition coating compositions by thetwo-component procedure can also be performed for example in such a waythat the nitrites and/or nitrates are in the presence of the ionicbinders that are in the non-aqueous phase and are converted to theaqueous phase along with them by dilution with water—after addition ofneutralising agent if this has not already-taken place. A cathodicelectrodeposition binder dispersion containing the nitrites and/ornitrates is obtained in this process. A pigmented cathodicelectrodeposition coating composition or bath can then be produced froma cathodic electrodeposition binder dispersion thus obtained by mixingwith a separate pigment paste. Alternatively, the two-componentprocedure can also be performed in such a way that an aqueous pigmentpaste containing nitrites and/or nitrates is added to a cathodicelectrodeposition binder dispersion.

The nitrites and/or nitrates can also be added separately to thecathodic electrodeposition coating compositions. It is also possible forexample to perform the separate addition subsequently, to cathodicelectrodeposition baths ready for coating. The nitrites and/or nitratesare converted to a water-dilutable form for this purpose; the separate,in particular subsequent addition can for example be performed as partof an aqueous pigment paste, produced separately for example, or thenitrites and/or nitrates can be added by means of a water-dilutablebinder, in particular as a component of a cathodic electrodepositionbinder dispersion or in an aqueous cathodic electrodeposition pasteresin or with the aid of suitable emulsifiers, for example by theprinciples described in the previous paragraph.

According to the invention cathodic electrodeposition coating films forexample in a dry film thickness of 10 to 30 μm are applied to variouselectrically conductive substrates or substrates rendered electricallyconductive, in particular metal substrates, from the cathodicelectrodeposition coating compositions containing the nitrites and/ornitrates and stoved in indirectly heated circulating air ovens at objecttemperatures of for example 160 to 190° C. The term “indirectly heatedcirculating air ovens” refers to circulating air ovens in which no wastegases are introduced into the circulating air of the oven and which arepreferably operated without or with only a small proportion of freshair, as is the case with the indirectly heated circulating air ovensoperated in industrial practice. The volume content of fresh air,relative to the circulated volume of circulating air per unit time, isbelow 20%, preferably below 10%. In the process according to theinvention the ratio during stoving of oven capacity to cathodicelectrodeposition lacquer surface area to be stoved is preferably up to2, for example 0.2 to 2 cubic metres per square metre or less. Thedimensions can be clarified by reference to an example from standardautomotive finishing: for example an industrially operated circulatingair oven with a capacity of 1000 cubic metres contains a total of 25 carbodies each displaying 80 square metres of cathodic electrodepositioncoating film to be stoved, the circulating air output is 150,000 cubicmetres per hour with a waste air and fresh air output of 12,000 cubicmetres each per hour. To simulate the stoving process in an indirectlyheated circulating air oven operated in industrial practice a laboratorycirculating air oven can be used, the proportion of fresh air in whichcan be restricted to below 20, preferably below 10% and in which a ratioof 0.2 to 2 cubic metres of oven capacity per square metre of cathodicelectrodeposition coating to be stoved is preferably maintained.

The process according to the invention or the use according to theinvention is suitable in particular for the motor vehicle sector, forexample for the production of an anti-corrosive cathodicelectrodeposition primer on vehicle bodies or vehicle body components,which are then provided with further coating films, in particularunderbody sealant films, for example.

The conventional underbody sealant films used in vehicle finishing canbe applied. Examples include coating compositions based on polyvinylchloride (PVC) plastisols. These are applied in particular to locationsin the vehicle underbody area that are at risk of impact from flyingstones. They are generally applied in thick coats, for example from 0.5to 3 mm.

Without giving a definite explanation, it is assumed as a theoreticalexplanation that the nitrites and/or nitrates co-deposited in theprocess according to the invention as a component of the cathodicelectrodeposition coating film decompose at the air temperatures of forexample 150 to 220° C. that prevail during stoving to release nitrogenoxides, referred to below as NO_(x), and the NO_(x), given off into thecirculating air in the oven gives rise to an improved or adequateadhesion of coating films that are subsequently applied.

The process according to the invention ensures a good adhesion ofsubsequent coating films, such as in particular underbody sealant films,for example, that are applied to cathodic electrodeposition coatingfilms stoved in indirectly heated circulating air ovens. Conceivablemeasures for improving adhesion such as the use of expensive bondingagents in the coating compositions used for application of thesubsequent coating films can also be avoided.

EXAMPLE 1 Production of Bismuth Lactate

901 parts of a 70 wt. % solution of lactic acid in water are heated to70° C. 466 parts of commercial bismuth oxide (Bi₂O₃) are added inportions with stirring. After stirring for a further 6 hours at 70° C.the batch is cooled to 20° C. and left for 12 hours without stirring.Finally the deposit is filtered off, washed with a little water andethanol and dried at 50° C.

EXAMPLE 2 Production of a CEC Dispersion

-   a) 832 parts of the monocarbonate of an epoxy resin based on    bisphenol A (commercial product Epikote 828) are mixed with 830    parts of a commercial polycaprolactone polyol (commercial product    CAPA 205) and 712 parts of diglycol dimethyl ether and reacted at 70    to 140° C. with 0.3% BF₃ etherate until an epoxy value of 0 is    reached. 307 parts of a reaction product of 174 parts of toluylene    diisocyanate (2 equivalents of NCO) with 137 parts of 2-ethyl    hexanol with an NCO content of 12.8% are added to this product    (solids content 70%, 2 equivalents of carbonate) at 40 to 80° C. in    the presence of 0.3% Zn acetyl acetonate as catalyst. The reaction    is continued until an NCO value of 0 is reached and the solids    content then adjusted to 70% with diglycol dimethyl ether.-   b) 618 parts of a reaction product of 348 parts of toluylene    diisocyanate (80% 2,4-isomer; 20% 2,6-isomer) with 274 parts of    2-ethyl hexanol with a residual NCO content of 12.8% are slowly    added to 1759 parts of a biscarbonate of an epoxy resin based on    bisphenol A (commercial product Epicote 1001) at 60 to 80° C. The    reaction is continued until an NCO value of 0 is reached and the    solids content then adjusted to 70% with diglycol dimethyl ether.-   c) 622 parts of the reaction product of 137 parts of 2-ethyl hexanol    with 174 parts of toluylene diisocyanate (NCO content 12.8%) are    added to 860 parts of bishexamethylene triamine dissolved in 2315    parts of methoxy propanol at a temperature of 30° C. and reacted    until an NCO content of 0 is obtained. 4737 parts of the reaction    product b) and 3246 parts of the reaction product a) (70% in    diglycol dimethyl ether in each case) are then added and reacted at    60 to 90° C. The reaction is terminated at an amine value of 32 mg    KOH/g. The resulting product is distilled off in vacuo down to a    solids content of 85%.-   d) Neutralisation is performed with 30 mmol formic acid/100 g resin.    The product is then heated to 70° C. and bismuth lactate added in    portions with stirring in a quantity such that 1 wt. % bismuth is    present relative to the solids content in the batch. Stirring is    then continued for a further 6 hours at 60° C. and the product    cooled. It is converted with deionised water to a dispersion with a    solids content of 40 wt. %.

EXAMPLE 3 Production of a Pigment Paste

15 parts acetic acid (50%), 30 parts of a commercial wetting agent (50%)and 350 parts deionised water are added to 223 parts of the paste resinaccording to EP-A-0 469 497 A1 example 1 (55%) in a high-speed mixer.12.3 parts of carbon black and 430 parts of titanium dioxide are added.The solids content is adjusted to 53 wt. % with deionised water and itis ground in a bead mill. A stable pigment paste is obtained.

EXAMPLE 4 Production of a Pigment Paste

Example 3 is repeated, whereby 20.5 parts of 65 wt. % cellulose nitrate(65 parts cellulose nitrate with a nitrogen content of 11 wt. %, wettedwith 35 parts butanol) are added before addition of the acetic acid.

EXAMPLE 5 Production of a CEC Bath and Coating, Comparison

A CEC bath with a solids content of 20 wt. % and a ratio by weight ofpigment to binder of 0.5:1 is produced by conventional means by mixingthe CEC dispersion from example 2 with deionised water, adding thepigment paste from example 3 and stirring well. Using the CEC bathadjusted with formic acid to an acid content of 35 milliequivalents/100g solids, 10 sheets (measuring 10 cm by 20 cm) of conventionalphosphated car body steel were coated by cataphoresis in a dry filmthickness in each case of 20 μm and stoved for 30 minutes at 160° C.(object temperature) in an electrically heated laboratory circulatingair oven with a capacity of 0.5 cubic metres (air temperature 220° C.,fresh air proportion limited to below 8%).

EXAMPLE 6 According to the Invention

Example 5 is repeated with the difference that the pigment paste fromexample 4 is used in place of the pigment paste from example 3. The CECbath contains 1.5 wt. % cellulose nitrate, calculated with respect tothe resin-solids.

EXAMPLE 7 Comparison

Example 6 is repeated with the difference that the laboratorycirculating air oven is operated with the maximum supply of fresh air.

CEC-coated sheets obtained in examples 5 to 7 are each coated with a PVCplastisol-based commercial underbody sealant material in a filmthickness of 2 mm using a knife and stoved for 20 minutes at 140° C.(object temperature) in order to solvate the plastisol. Parallelincisions are made in the solvated plastisol film at intervals of 1.5cm. At the edge between two incisions the solvated plastisol iscarefully detached from the CEC coating with a knife in order to obtaina tab. An attempt is then made to peel away the plastisol film by hand.The adhesion is acceptable only in the case of example 6. In examples 5and 7 the solvated plastisol film can be peeled away from the CECsubstrate.

1. A process for the production of an electrodeposition coating filmwith improved adhesion for subsequent coats comprising the steps ofcathodically depositing a coating film from a cathodic electrodepositioncoating composition onto an electrically conductive substrate and bakingthe film in an indirectly heated circulating air oven; wherein aproportion of fresh air introduced into the oven is 0 to 20 volume % ofthe circulating air in the oven; and wherein the cathodicelectrodeposition coating composition comprises resin solids and atleast one water-insoluble nitrogen compound selected from the groupconsisting of organic ester nitrites, organic ester nitrates andmixtures thereof.
 2. The process of claim 1 wherein the water insolublenitrogen compound is present in the cathodic electrodeposition coatingcomposition in an amount of 0.05 to 0.5 wt. %, calculated as nitrogenpresent in the form of organically bonded nitrite, nitrate or mixture ofnitrite and nitrate, relative to the resin solids of the coatingcomposition.
 3. The process of claim 2 wherein the water insolublenitrogen compound is selected from the group consisting of esters ofnitrous acid and a mono-hydroxy functional polymer, esters of nitrousacid and a polyhydroxy functional polymer, esters of nitric acid and amono-hydroxy functional polymer, esters of nitric acid and a polyhydroxyfunctional polymer and any mixtures thereof.
 4. The process of claim 3wherein the water insoluble nitrogen compound consists of a cellulosenitrate.
 5. The process of claim 4 wherein the cellulose nitrate has acontent of nitrogen bonded as nitrate of 6.7 to 12.5 wt. %, relative tothe resin solids of the coating composition.
 6. The process of claim 1wherein the ratio of oven capacity to surface area of the electricallyconductive substrate being coated with the electrodeposition coatingcomposition is up to 2 cubic meters per square meter of substrate. 7.The process of claim 1 wherein more than one electrodeposition coatingfilm is applied to the substrate.
 8. The process of claim 1 wherein theelectrodeposition coating film is applied to a motor vehicle body and anunderbody sealant film is then applied to a portion of the motor vehiclebody.
 9. The process of claim 1 wherein the electrodeposition coatingfilm is applied to a motor vehicle body part and an underbody sealantfilm is then applied to a portion of the motor vehicle body part.